台灣中部蓮華池森林樹種群聚與地形、水分有效性及樹種耐旱性的關係

Relationships of Tree Species Associations with the Topography, Water Availability, and Species Drought Tolerance in the Lienhuachih Forest of Central Taiwan

郭耀綸(Yau-Lun Kuo) ； 張勵婉(Li-Wan Chang) ； 林易養(Yi-Yang Lin) ； 余尚鈺(Shang-Yu Yu)

《台灣林業科學》 35卷2期 (2020/06) Pp. 123-142

https://doi.org/10.7075/TJFS.202006_35(2).0002

摘要

台灣中部蓮華池森林在山坡不同位置的生育地有不同的樹種群聚。本研究探討該森林樹種群聚與地形、水分有效性及樹種耐旱性間的關係。試驗樹種包括分布在山脊、坡面、溪谷三處生育地的52樹種。本研究藉土壤含水率及植株黎明前葉部水勢（Ψ_(pd)），指示各生育地的水分有效性。藉各樹種的膨壓喪失點葉部水勢（π_(tlp)），比較樹種間及不同樹種群聚間葉部耐旱性的差異。結果發現，在乾季期間山脊生育地的土壤含水率及植株的Ψ_(pd)，均顯著低於溪谷生育地。供試所有樹種乾季時π_(tlp)在-2.98～-2.03MPa範圍，平均為-2.49±0.03 MPa，以大丁黃、南投石櫟、臺灣紅豆樹有最高的葉部耐旱性。山脊、坡面、溪谷三處生育地的樹種群聚，乾季期間的平均π_(tlp)分別為-2.66±0.05、-2.50±0.07、-2.25±0.07MPa，以山脊群聚樹種的葉部耐旱性顯著最高。依據π_(tlp)區分樹種耐旱性等級，供試樹種中有29種歸類為「耐旱」等級，另23種則屬於相對較不耐旱的「中等耐旱」等級。乾季期間大多數樹種的π_(tlp)顯著低於雨季時，顯示葉部耐旱性呈現季節性馴化。此外，同一樹種沿著水分有效性梯度，植株葉部耐旱性有明顯的空間馴化，生長在山脊植株的π_(tlp)顯著低於溪谷同種的植株。乾季期間生長在山脊18樹種的π_(tlp)與Ψ_(pd)呈顯著負相關，顯示生理耐旱性較高的樹種，形態上可能也具根深性。本研究發現，生育地水分有效性及樹種葉部耐旱性，是影響蓮華池森林樹種群聚於生育地空間分化眾多機制中重要的兩項。

關鍵字

生育地水分有效性 ； 葉部耐旱性 ； 膨壓喪失點葉部水勢 ； 黎明前葉部水勢 ； 季節性馴化

並列摘要

Different species associations are situated in habitats at various slope positions in the Lienhuachih forest of central Taiwan. This research investigated relationships of tree species associations with the topography, water availability, and species drought tolerance of this forest. In total, 52 species distributed in ridge, slope, and valley habitats were studied. The soil water content and predawn leaf water potential (Ψ_(pd)) were adopted to indicate the water availability of each habitat. The leaf water potential at the turgor loss point (π_(tlp)) was used to compare differences in leaf drought tolerance among species and species associations. Results showed that the soil water content and Ψ_(pd) of species in the ridge habitat were significantly lower than those in the valley habitat. Values of the π_(tlp) of all species during the dry season ranged -2.98~-2.03 MPa, with a mean π_(tlp) of -2.49±0.03 MPa. Among the studied species, Euonymus laxiflorus, Lithocarpus nantoensis, and Ormosia formosana had the highest leaf drought tolerance. Species associations of ridge, slope, and valley habitats showed mean π_(tlp) values of -2.66±0.05, -2.50±0.07, and -2.25±0.07 MPa, respectively, with the species association of the ridge habitat having the highest leaf drought tolerance. After adopting values of the π_(tlp) to categorize drought tolerance classes of the 52 tested species in the Lienhuachih forest, 29 species were classified into the 'drought-tolerant' category, and the other 23 species were 'mid-drought tolerant' with relatively less tolerance. The π_(tlp) of every species was significantly lower during the dry season than the rainy season, indicating seasonal acclimation of the leaf drought tolerance. In addition, there was also significant spatial acclimation in the leaf drought tolerance along the water availability gradient, i.e., π_(tlp) values of individuals growing in the ridge habitat were all significantly lower than those of individuals of the same species growing in the valley habitat. During the dry season, the Ψ_(pd) and π_(tlp) of 18 species growing in the ridge habitat appeared to be negatively correlated, indicating that species with high physiological drought tolerance might also have deeper root systems. This research found that habitat water availability and leaf drought tolerance are two important mechanisms, among others, driving habitat divergence of tree species associations in the Lienhuachih forest.

並列關鍵字

habitat water availability ； leaf drought tolerance ； leaf water potential at turgor loss point ； predawn leaf water potential ； seasonal acclimation